There’s something mysterious happening in Iowa—a massive data center is going up, thought to be the home of a next-generation facility from Apple, Google, or another major provider.

The Planning and Zoning Commission of Altoona, a suburb of Des Moines, has approved a 25 percent bump in the proposed size of the three buildings scheduled for construction on the site. The mysterious company has expanded its building plans by nearly 300,000 square feet, for a total of 1.4 million square feet, reported the Des Moines Register.

To put this so-called “Project Catapult” in context, Facebook’s Prineville datacenter (as planned in 2010) totaled just over 300,000 square feet—even after the social network announced plans to double the facility’s size. Apple’s own facility in Prinevillle, which will be powered exclusively by renewable energy sources, will total about 338,000 square feet. And Apple’s Maiden, N.C. facility, one of the largest privately owned data facilities, covers 500,000 square feet and cost about $1 billion. Compare that to the original Altoona site plan, which called for one 350,000 square-foot building and two buildings at 380,000 square feet, and it’s clear something big is going on here.